error instanceof BiometryError, error.code typing about capacitor-biometric-auth

[aparajita]

Thanks for the request, v6.0.0 has just been released that throws an instance of BiometryError from authenticate(), and BiometryError.code is typed as BiometryErrorType.

[aparajita]

The error thrown by any Capacitor plugin is actually an instance of CapacitorException. I'm not sure if that's something that happened after I originally wrote this plugin, because I don't remember that being the case.

Even if I intercept the exception and throw a BiometryError instance, you would still need a type guard because Typescript does not type catch variables. So you can achieve what you want now like this:

interface TypedBiometryError extends BiometryError {
  code: BiometryErrorType
}

async function showErrorAlert(error: TypedBiometryError): Promise<void> {
  await showAlert(`${error.message} [${error.code}].`);
}

function isBiometryError(error: unknown): error is TypedBiometryError {
  return error instanceof CapacitorException;
}

function isBiometryError(error: unknown): error is TypedBiometryError {
  return error instanceof CapacitorException;
}

async function authenticate(): Promise<void> {
    try {
      await BiometricAuth.authenticate({
        allowDeviceCredential: true,
      });
    } catch (error) {
      // The type guard will ensure you compare error.code against a valid BiometryErrorType value
      if (isBiometryError(error) && error.code === BiometryErrorType.biometryNotEnrolled) {
        showAlert(error)
      }
      throw error;
    }
}

[aparajita]

In any case I should add that type guard function to the plugin and type code as BiometryErrorType.